Force-balance pneumatic regulator with resilient cross fulcrum, having high sensibility and precision and easy, continuous gain regulation

ABSTRACT

A pneumatic force-balance regulator is described that has a pair of bellows which respectively support members, movable in response to differences in the external and internal pressures on the bellows, that are connected through struts to a balance mounted to oscillate around a resilient cross fulcrum so that the regulator gain may vary with continuity and the axes of the struts lie in the plane containing the axis of oscillation of the balance so that parasitic forces, acting on the struts along their axes, do not affect the equilibrium of the balance.

United States Patent Bergamini [45] Aug. 8, 1972 [54] FORCE-BALANCEPNEUMATIC 7 2,365,573 12/ 1944 McGay ..73/407 REGULATOR WITH RESILIENTCROSS 2,816,444 l2/ 1957 Gomez ..73/407 FULCRUM, HAVING HIGH 3,126,7443/1964 Hermanns ..73/407 SENSIBILITY AND PRECISION AND 3,078,719 2/1963Cordero et al ..73/407 EASY, CONTINUOUS GAIN 3,354,722 11/1967 Waite etal. ..92/37 REGULATION 3,451,272 6/ 1969 Frey et al ..73/410 [72]Inventor: Giorgio Bergamini, Corso Sicilia, 56 Primary Examiner Marfin RSchwadron Italy Assistant Examiner-Leslie J. Payne [22] Filed: Nov. 6,1970 Attomey-Ralph M. Watson 3 [21] Appl. No.: 87,495 I I [57] IABSTRACT:

A pneumatic force-balance regulator is described that [30] ForeignApplmmon Pmmvty Data has a pair of bellows which respectively supportmem- Sfipt. ll, bets movable response to difi'erences in the exter.

, nal and internal pressures on the bellows, that are con- }.LE.CCII...L nected through truts to a mounted to oscil- I! late around aresilient cross fulcrum so that the regula [58] Fleld OI Search l37/82,84; 73/410, 407; tor g y y with continuity d h axes f the 7 92/37 39struts lie in the plane containing the axis of oscillation of thebalance so that parasitic forces, acting on the [56] References Citedstruts along their axes, do not affect the equilibrium of UNITED STATESPATENTS the balance- 2,75l,457 6/1956 Donaldson ..92/37 X 2 Claims, 3Drawing figures PAIENTEDAus 8 I972 3,682,048

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PATENTEDAus 8 m2 FORCE-BALANCE PNEUMATIC REGULATOR WITH RESILIENT CROSSFULCRUM, HAVING HIGH SENSIBILITY AND PRECISION AND EASY,

CONTINUOUS GAIN REGULATION I The present invention relates to aforce-balance pneumatic regulator with resilient cross fulcrum, which,by eliminating clearances, frictions and undesired moments, presents ahigh sensitivity and precision and allows an easy continuous gainregulation.

It is known that in the designing of a force-balance pneumatic regulatorthe following problems above all have to be solved:

a. realization of a balance whose fulcrum present neither. clearancesnor frictions in such a way to make possible a high sensitivity;

b. the effective areas of the measurement elements (bellows) of thepressures compared two by two, must be the more equal possible to reacha high precision of regulation;

c. the ratio of the thrusts acting on the balance (and i.e. theregulator gain) has to be varied in a simple way and with continuity, byvarying the balance fulcrum position, without introducing parasiticforces on the same balance which would reduce noticeably both thesensitivity and the precision of regulation of the regulator. 1

Now, the prior art knows different types of pneumatic regulators havingforce-balance, none of them, however, is able to satisfy at the sametime the three above-mentioned conditions.

Thus are known pneumatic regulators which adopt as fulcrum,ball'bearings, hard stones or pairs of little rolls, which allow tosolve well condition but do not I satisfy well condition (a). Saidregulators therefore do not present a high sensitivity.

Other pneumatic regulators having force-balance adopt resilient crossfulcra, which satisfy very well condition (a) but make extremelydifficult the solution of problem (c), which is really resolved by meansof complex devices, noticeable compromises and to detriment of theregulation precision. Therefore, these regulators, besides to a limitedprecision, do not allow an easy, continuous gain regulation. As far ascondition (b) is concerned, have been designed force-balanced pneumaticregulators wherein the equality of the effective areas is reached bymaking use only of a bellow with which the pressures are comparedbetween the inside and the outside of the bellow self. These regulatorshave however this drawback: the connection between the bellow, placedinside a pressure chamber, and the balance which is outside saidchamber, introduces, due to the frictions, some disturbances whichresult in a noticeable reduction of the precision of regulation of thesame regulators.

The object of the present invention is that of obviating all theabove-mentioned drawbacks and therefore the accomplishment of aforce-balance pneumatic regulator which, by satisfying all the threeabove-mentioned conditions, present a high sensitivity and precision andallows an easy and continuous regulation of its gain. This is achievedby adopting a resilient cross fulcrum and only a bellow for each pair ofpressures to be compared.

According to an essential feature of the invention, a resilient crossfulcrum of particular structure is utilized, which allows to vary withcontinuity the regulator gain by letting simply rotate said fulcrumaround an axis perpendicular to the oscillation axis of the balanceconnecting the two bellows.

Another feature of the invention is given by the fact the connection ofthe bellows to the balance is realized by means of through struts whoseaxes lie in the plane containing the .balance of oscillation axis,whereby the parasitic thrusts acting on said through struts and relativeseal membranes, being directed along the axes of the struts, do not atall effect the equilibrium of the balance and therefore the precision ofregulation of the regulator.

According to a further feature of the invention it is possible to varythe regulator gain also when the regulator is in operation, as momentsintroduced by friction on the balance by the rotation of resilient crossfulcrum are compensated by a tie rod whose axis lie in the planecontaining the balance oscillation axis.

The. invention is now illustrated in detail with reference to theaccompanying figures which represent a preferred embodiment of theinvention, given only by unrestrictive example, as technical andconstructional modifications may be brought without departing from thescope of the present invention.

FIG. 1 shows a cut-away front section of the forcebalance pneumaticregulator with resilient cross fulcrum, according to the invention.

FIG. 2 shows a broken-away perspective view of the resilient crossfulcrum according to the invention.

FIG. 3 shows a cut-away top view of the pneumatic regulator of FIG. 1.

Referring to the figures, reference numeral 1 indicates the supportingplate of the pneumatic regulator on which, by means of threaded screws 2and suitable gaskets, boxes 3 and 4 are hermetically fixed. In each ofsaid boxes 3 and 4 and in suitable cavities 5 and 6 made in supportingplate 1 are then housed respectively moving equipments 7 and 8 insidewhich one of the ends of bellows 9 and 10 is respectively welded,whereas the other ends of the above-mentioned bellows are hermeticallyfixed to the heads of boxes 3 and 4 respectively. In such a way fourchambers are defined, two of which, 11 and 12 respectively, insidebellows 9 and 10, and two, 13 and 14 respectively, outside said bellowswhose effective areas are perfectly equal between them.

Two helical springs 15 and 16, respectively inside bellows 9 and 10, arethen retained at one end by spring bearings 17 and 18 respectivelyscrewed at bottom of the moving equipments and at the other end retainedby other spring bearings 18 and 19 respectively, which may be screwed onthe adjusting screws 20 and 21 supported by the heads of boxes 3 and 4.

Said adjusting screws 20 and 21, by varying the tension of the springs15 and 16 and consequently the position uprightly of the movingequipments 7 and 8 allow the zero setting of the regulator. The twomoving equipments 7 and 8 are then solidly connected to balance 22 ofthe regulator by means of struts 23 and 24 respectively, which,extending in a perpendicular direction to the movement of the mobileequipments and protruding from holes placed in boxes 3 and 4, arescrewed on said balance by means of screws 25. To

cause the two chambers 13 and 14 be hermetically closed, the twoabove-mentioned holes of boxes 3 and 4 are closed by elastic sealmembranes 26 which allow little vertical shiftings of through struts 23and 24 and therefore of mobile equipments 7 and 8.

Whereas set pressure is conveyed into chamber 13, through duct 27, thepressure to be controlled and to be kept always equal to the setpressure, is on the contrary conveyed into chamber 11 through duct 28.An inequality between the two above-mentioned pressures will resulttherefore in a vertical shift of the mobile equipment 7 and i.e. willgive rise to a force which, transmitted by strut 23 to balance 22, willunbalance the balance self, by letting it oscillate around its fulcrum.

Said unbalance of the balance will be then compensated by the action ofother two reaction pressures which are produced by a pneumatic relay(not shown in the figures) driven by nozzle 29 shutter plate system, thefunction of said shutter plate being effected by the same balance 22.

These reaction pressures conveyed into chambers 12 and 14 respectively,through ducts 30 and 31, bringing again the balance in a balanceposition, will compel the pressure to be controlled to become and tomaintain itself equal to the set pressure.

The balance fulcrum 22, according a feature of the present invention, isthen formed by two platforms 32 and 33 suitably shaped as better seen inFIG. 2 and having two pivots 34 and 35 jointed to them. Upper platform33 is inserted with its pivot 35 in a suitable hole made in an overheadplate 36, solidly connected to sup-- porting plate 1 by means of screwedlittle columns 37, and is fixed to said overhead plate by nut 38 and bycarriage spring 39. Likewise, lower platform 32 is inserted with itspivot 34 in a suitable hole of balance 22 and fixed thereto by nut 40and bycarriage spring 41. In such a way two platfon'ns 32 and 33 aremade integral respectively with balance 22'and with supporting plate 1but they are free of rotating around a rotation vertical axis aa passingthrough their pivots. Each platform has then at the ends of its diametera pair of flexible blades, double L shaped whereby the two platforms arejoined between them by a cross resilient constraint. More precisely,flexible blades 42, each of them having a side of double L welded to thevertical wall of platform 33 (see FIG. 2), are let in through the slotof flexible blades 43, of platform 32 and are welded with other sides ofthe double L to vertical walls 44 of platform 32; flexible blades 43,welded in a side of the double L on the upper wall of platform 32, areon the contrary welded with other sides of double L under the lower wallof platform 33.

With such a constraint the two platforms 32 and 33 are so made integralbetween them as far as the rotation around rotation axis an is concernedand moreover oscillations of lower platform 32 are made possible, andconsequently of balance 22, around axis bb passing through the bladesand perpendicular to rotation axis aa, Said oscillation axis bbrepresents just the axis around the which balance 22 will oscillate torestore the balance between the forces generated by the pressures actingon the chambers 1 l, 12, 13 and 14.

Now, according to a constructional feature of the invention, oscillationaxis bb lies always in the plane (designated cc in FIG. 1) passingthrough the center line of through struts 23 and 24. This has, as aresult,

the elimination of all the disturbances which arise in usual regulatorsdue to the connection if a bellows inside a pressure chamber to abalance outside said chamber, disturbance which results in a noticeablelowering of the precision of regulation of the regulator self. As amatter of fact, the parasitic thrusts exerted by the pressures at stakeon the through struts 23 and 24 and on the relative resilient sealmembranes 26, result in direct forces along the axis of the strutsselves and i.e. in forces which, by acting in the same plane cccontaining oscillation axis bb, cannot absolutely generate moments whichtend to let oscillate balance 22 around axis bb and therefore to disturbthe equilibrium of the balance self.

On the other hand, by adopting the above-mentioned cross fulcrum, thegain of the regulator may be now easily regulated with continuity byletting simply rotate the two platforms 32 and 33 around their rotationaxis aa. In this way, as matter of fact, the oscillation axis bb is putto rotation and consequently change the values of the distances d and e(see FIG. 3) from said axis bb of points F and G.

As these points F and G are the points of applications of the forcesexerted on balance 22 respectively by the pressures acting on thebellows 10'and by the pressures acting on the bellows 9 and thereforedistances d and e are lever arms of said forces it is evident that, byvarying said lever arms, the moments exerted on the balance by saidforces are varied and consequently the ratio of the thrusts acting onthe balance and i.e. the gain of regulator is varied.

In order to facilitate the rotation operation of the platforms aroundaxis aa as to regulate the regulator gain, to pivot 35 of upper platform33, between nut 38 and carriage spring 39, is keyed a rack 45 meshed ona toothed small wheel 46 mounted idle on overhead plate 36. In such away to vary the regulator gain it is sufficient to shift angularly rack45.

To make possible the gain regulation also when the regulator is inoperation and therefore to eliminate the moments introduced by frictionon balance 22 by the rotation around axis aa of resilient cross fulcrum,on the end of the balance in correspondence of nozzle 29 is screwed ablock 46 to which is hinged an end of a tie rod 47 the other end ofwhich is hinged to another block 48 firmly screwed to supportingplate 1. The system of two blocks and of the tie rod is then arranged insuch a way that the axis of tie rod lies on already cited plane cccontaining oscillation axis bb so that the torque generated by itcompensates always the abovementioned friction moments.

What I claim is:

l. A force-balance pneumatic regulator comprising a supporting plate, apair of boxes fixed to said supporting plate to provide air chambers,bellows moving equipment contained in each of said boxes, a balance, asupporting plate, a resilient cross fulcrum for said balance comprisingupper and lower platforms pivoted, respectively, to said balance andsaid overhead plate and solidly connected to said supporting plate, andpairs of double L-shaped flexible blades welded at the ends of adiameter of said platforms to join them together, and means to vary thegain of said regulator.

- 2. A force-balance pneumatic regulator comprising a supporting plate,a pair of boxes fixed to said supportrack keyed to the pivot for saidupper platform, a toothed idler gear mounted on the overhead plate andmeshing with said rack, and a tie rod hinged to said balance and to thesupporting plate so that its axis lies on the plane containing theoscillation axis of the balance.

1. A force-balance pneumatic regulator comprising a supporting plate, apair of boxes fixed to said supporting plate to provide air chambers,bellows moving equipment contained in each of said boxes, a balance, asupporting plate, a resilient cross fulcrum for said balance comprisingupper and lower platforms pivoted, respectively, to said balance andsaid overhead plate and solidly connected to said supporting plate, andpairs of double L-shaped flexible blades welded at the ends of adiameter of said platforms to join them together, and means to vary thegain of said regulator.
 2. A force-balance pneumatic regulatorcomprising a supporting plate, a pair of boxes fixed to said supportingplate to provide air chambers, bellows moving equipment contained ineach of said boxes, a balance, a supporting plate, a resilient crossfulcrum for said balance comprising upper and lower platforms pivoted,respectively, to said balance and said overhead plate and solidlyconnected to said supporting plate, and means to vary the gain of saidregulator comprising a rack keyed to the pivot for said upper platform,a toothed idler gear mounted on the overhead plate and meshing with saidrack, and a tie rod hinged to said balance and to the supporting plateso that its axis lies on the plane containing the oscillation axis ofthe balance.